Fluorinated surfactants have been widely used, for example, as foaming agents and leveling agents for many years. The foaming and leveling properties of fluorinated surfactants have made them useful in many industries (e.g., oil and gas and textiles) for many applications (e.g., industrial coatings).
Foams are useful in various operations involving hydrocarbon-producing wells (e.g., oil or natural gas wells), including enhanced oil recovery, fracturing, drilling, and completion operations. Foamed fluids may have several advantages over non-foamed fluids. For example, the volume of liquid in a foamed fluid is less than in non-foamed fluids, and as a result, less fluid loss to permeable subterranean formations occurs when a foam is used. Further, foamed fluids are typically more easily removed from a geological formation following an enhanced oil recovery, fracturing, or completion operation than non-foamed fluids. Foamed fluids (including either gelled or non-gelled fluids) also tend to have a greater ability than their non-foamed counterparts to suspend and transport particulate materials (e.g., proppants, gravel, released fines, and drilling cuttings) that are used or produced in fracturing, drilling, or completion operations. Foams also have lower densities than non-foamed drilling fluids, and the use of foams typically lowers the formation damage potential when drilling in underbalanced conditions (i.e., when the pressure in the drilling fluid is lower than the pore pressure in the surrounding rock).
Liquids utilized as the liquid phase in foams employed in gas- or oilfield operations include water, hydrocarbons, and aqueous alcohol solutions. The use of one or more hydrocarbons in the liquid phase of foamed fluids for subterranean formation treatments is advantageous when the subterranean formation is sensitive to the intrusion of water foreign to the formation. Such water-sensitive formations generally contain clays that are irreparably damaged upon foreign water contact due to the swelling of the clays and/or the migration of fines as a result thereof.
In a foam, gas bubbles are separated from each other by thin liquid films. Typically, surfactants stabilize foams by adsorbing at the interface of the bubbles and the liquid films and providing a barrier to coalescence of the bubbles. It is typically more challenging to form hydrocarbon foams than to form aqueous foams. Unlike water, which has a high surface tension and can dissolve charged species, hydrocarbons generally do not have properties that prevent the coalescence of gas bubbles.
Some fluorinated surfactants are known to produce stable hydrocarbon foams. Traditionally, many of the widely available fluorinated surfactants include long-chain perfluoroalkyl groups, for example, perfluorooctanesulfonamide groups. Recently, however, there has been an industry trend away from using perfluorooctyl fluorinated surfactants, which has resulted in a need, for example, for new types of surfactants that can produce hydrocarbon foams.
One nonionic polymeric fluorinated surfactant having perfluorobutanesulfonamido-containing repeating units and a weight average molecular weight of about 15,000 grams per mole has been used as a hydrocarbon foaming agent in drilling fluids and in enhanced oil recovery fluids added to injection wells.